EMT - UL Heads Up [RE-wrenches]

Jason Fisher jfisher at nahbrc.org
Tue Mar 16 07:34:28 PST 2004


A not so often followed NEC requirement is to provide expansion fittings
on longer PVC runs (NEC 1999 347-9, don't have 2002 with me). These
fittings (slip coupled pipe with o-rings and Vaseline, that are still
not "watertight"!) are hard to find in supply shops but are essential
for applications like wiring piers. Generally, I'd hope we keep our runs
shorter but one still should keep in mind just how much this stuff moves
over temperature swings (see table). Frequently, you'll find pipes
popped out of glued connectors at enclosures. While one might blame the
helper for not putting enough glue on the joint, often times this is due
to the conduit being installed during the hot summer, strapped down
tight, then shrinking during the winter. You also see this a lot when
PVC comes out of the ground, especially if it wasn't supported by
undisturbed earth. And yes, all the old PVC I've messed with shatters
easily.

It is sad to hear that the rumors of this EMT-fitting issue are now
being played out in CA. I do not look forward to the day when inspectors
here start pulling this out of their hats. Anyone who has done
electrical service work on equipment in wet applications knows that no
conduit system is watertight, even the expensive PVC coated steel. The
conductors need to be rated wet for a reason and we have always drilled
weep holes in our exposed boxes. I had an inspector once, take issue
with this (not in line with the box's listing) and suggest that we
rather leave out a threaded plug and install screening to keep out the
bugs. Huh? OK, thanks for the tip. I said I'd make sure I did that "next
time".

Jason Fisher

-----Original Message-----
From: William Miller [mailto:wrmiller at slonet.org] 
Sent: Monday, March 15, 2004 10:27 PM
To: RE-wrenches at topica.com
Subject: [SPAM] - RE: EMT - UL Heads Up [RE-wrenches] - Email found in
subject

At 06:08 PM 3/15/2004, you wrote:

>I don't know if my experiences come from UV or heat-related exposures, 
>or a combination thereof.  What I do know is that I have seen and 
>replaced too many exposed horizontal PVC conduit installations with 
>sagging runs, split fittings, disfigured shapes, separated connections,


That's easy to fix!  Just strap the PVC to some EMT!

William

PS:  With PVC you can't ignore thermal expansion effects.  (Not so
familiar with EMT-- Is this also an issue?)  I don't ever figure any
pipe, on a roof or underground, will stay dry.  And it's true, PVC can
sag, it requires better support than EMT.

Wm

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